Allium L.

Scientific Description

Common name. Onion. Family Alliaceae.

Sometimes included in Liliaceae.

Habit and leaf form. Herbs (with annual leaves); laticiferous (mucilaginous). Perennial. Leaves basal (mostly), or cauline. Plants with a basal concentration of leaves (but sometimes the leaves long-sheathed so as to appear cauline). Young stems cylindrical, or flattened. Stem internodes solid, or hollow. Bulbaceous. Mesophytic, or xerophytic. Leaves alternate; distichous (commonly), or spiral; sessile (usually), or petiolate (rarely, e.g. Allium ursinum); sheathing. Leaf sheaths with free margins. Leaves aromatic (onion- or garlic scented, with allylic sulphides); simple; epulvinate. Leaf blades entire; flat, or solid; solid/angular (triquetrous); linear, or lanceolate, or ovate; ovate (narrowly), or linear (usually); parallel-veined; without cross-venules; sheathing to various heights of the scape. Leaf anatomy. Hairs absent. Stem anatomy. Secondary thickening absent.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Plants viviparous (commonly), or not viviparous. Floral nectaries present. Nectar secretion from the gynoecium (from septal nectaries). Entomophilous.

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in umbels (few to many-flowered). The terminal inflorescence unit cymose. Inflorescences scapiflorous; terminal; umbellate, representing one or more contracted, helicoid cymes; with involucral bracts (with two or more bracts, more or less fused and hyaline, enclosing the immature umbel); spatheate (with reference to the one to several spathal involucral bracts). Flowers pedicellate (rather slender); bracteate (1 or more, scarious, sometimes coloured spathe bracts per umbel); bracteolate (subtend pedicels), or ebracteolate; regular; 3 merous; cyclic; pentacyclic. Perigone tube present, or absent. Perianth of ‘tepals’; 6; 2 -whorled (3+3); isomerous; free, or joined; petaloid; similar in the two whorls; white, or violet, or blue, or purple, or yellow. Androecial members definite in number. Androecium 6. Androecial members adnate (at the base of the perigone); all equal; basally coherent, or free of one another; 2 -whorled (3+3). Androecium exclusively of fertile stamens. Stamens 6 (in 2 whorls); all more or less similar in shape; isomerous with the perianth; alterniperianthial; filantherous (the filaments flat). Filaments appendiculate (lateral teeth), or not appendiculate. Anthers dorsifixed; dehiscing via longitudinal slits; introrse. Gynoecium 3 carpelled. The pistil 3 celled. Carpels isomerous with the perianth. Gynoecium syncarpous; synstylovarious, or eu-syncarpous; superior. Ovary plurilocular; 3 locular; sessile. Gynoecium stylate. Styles 1; ‘gynobasic’ (or nearly so). Stigmas 1. Placentation axile. Ovules 2(–4) per locule; campylotropous (usually), or anatropous.

Fruit and seed features. Fruit non-fleshy; dehiscent; a capsule. Capsules loculicidal. Fruit 3–6 seeded. Seeds endospermic. Endosperm oily. Cotyledons 1. Embryo straight to curved. Testa encrusted with phytomelan.

Economic uses, etc. Onions, garlic, leek.

Etymology. From the Greek name for garlic, A. sativum.